This invention relates to improvements in steering column assemblies of the kind including a support bracket that permits collapse during a crash. It also relates to steering assemblies including a support bracket.
Steering column assemblies for automotive vehicles and the like are increasingly required to be adjustable for steering wheel height known as rake and, in many cases, steering wheel distance known as reach. This requires the column shroud, within which the steering column shaft attached to the steering wheel is rotatably located, to be fixed to the vehicle by a clamp mechanism which can be locked and unlocked to either prevent or permit adjustment of the column shroud position respectively.
One common arrangement uses a telescopic column shroud which comprises an inner member and an outer member—typically two elongate metal tubes—which slide one inside the other to permit reach adjustment. Fixing rails are welded to one of the tubes and are secured to a first support bracket by a releasable clamp mechanism. The support bracket is in turn secured to a relatively immobile part of the vehicle chassis, often by securing the first support bracket to a second support bracket that is fixed to the vehicle. When the clamp mechanism is clamped the fixing rail and support brackets are fixed relative to one another. When unclamped they can move relative to one another to permit the required reach adjustment.
Rake adjustment can be achieved by providing a support bracket that is shaped like an inverted U and includes vertically extending slots in its side arms through which the clamp mechanism passes. The clamp mechanism can be moved vertically within these slots, taking the column with it to adjust rake.
In the event of a crash it is desirable for the steering column assembly to collapse in a controlled manner. This helps to reduce the forces of a driver colliding with the steering wheel or its airbag. A steering column which is arranged so that it can move during an accident is known as a collapsible steering column assembly.
In one known arrangement the controlled collapse of a telescopically adjustable steering column assembly is enabled by frangibly connecting the U bracket to the vehicle, or to the second support bracket, using one or more frangible capsules. In a crash the forces on the U bracket are sufficiently high to cause it to break away from the capsules thus permitting the U bracket to move relative to the vehicle or second support bracket.
To control the movement of the column during collapse, some form of energy absorbing device is typically provided that acts between the U bracket and the vehicle body. The energy absorbing device in use absorbs energy in the event of a collapse of the steering assembly. In this context, a collapse is defined as movement of the shroud beyond its normal range of adjustment due to the application of force through the steering wheel along the axis of the steering column shaft. This force will typically arise if a drivers body is impacted on the steering wheel in a crash. For a steering column assembly that is adjustable for reach the normal range of adjustment will correspond to the allowable reach adjustment of the steering and this should not be opposed by the energy absorbing device, since that would make the steering difficult to adjust for reach.
The energy absorbing device controls the movement of the support bracket. For example, a deformable strap may be fixed to the U-Bracket and may slide over a fixed anvil, causing progressive distortion of the strap in order to absorb energy. Whilst this arrangement can be very effective it has been found that in some cases it can provide packaging issues.